Transmission of digital information and data between systems has become an essential part of commonly used systems, and in most cases users are not aware that the information has been transmitted in digital format. For the most part, it is difficult if not impossible for a user to perceive any indication that the transmission is digital rather than analog. In applications where the contents of the data transmission represent information like voice, sound, moving pictures, or sensor data, there is usually a requirement on delivery time, which will hereinafter be referred to as a "real-time" requirement.
Digital communication between devices distant from each other usually precludes the availability of identical sampling frequencies except for those cases where a distant clocking hierarchy structure has been defined and a common distributed clock source can be employed. In a variety of applications, the transmitter (data source) and receiver (data sink) operate at different sampling clock frequencies where the ratio between the frequencies is a non-integer. In some cases, there is no flexibility for the receiver clock to fine-tune or adjust to a common clock, or an integer product quotient, of the clock of the transmitter. That is, even though information is being transmitted at the same nominal sampling rate, when the local clocks are not the same, there will usually be a slight difference in the actual sampling rates. As a result, sampling at the sending terminal and reconstruction at the receiving terminal will be accomplished with a slight variance in the nominal sampling rates. Frequencies may also vary over temperature, part scattering, and time. For clock ratios with a fractional part, a rate exists at which sample overruns or underruns at the receiver input will occur. Those overruns and underruns are hereinafter referred to as sample slippage. Sample slippage generates objectionable distortion, for example, in the form of an audible click noise in audio transmissions and horizontal jitter in television systems.
Also, in some systems, the error due to slippage is cumulative and segments of transmitted information are backed-up and/or delayed. Over a period of time, such segments may eventually be periodically lost especially if the system is designed to re-synchronize or to attempt to re-synchronize itself to real time or to a master clock.
Thus, there is a need for a digital transmission system effective to reduce slippage signal distortions to a tolerable level, where the computational effort can be tailored to the required degree of accuracy in signal reproduction.